PHP warnings with first pubcookie login

Drupal 6.2 (error_reporting set to E_ALL & ~E_NOTICE in php.ini)
Profile module enabled
pubcookie-6.x-1.1 enabled, configured to use LDAP

I thought I submitted this problem earlier today, but I guess I didn't hit the submit button.

A first time pubcookie login generates these PHP warnings:

# warning: array_fill(): Number of elements must be positive in /home/web/html/techs/includes/database.inc on line 235.
# warning: implode(): Bad arguments. in /home/web/html/techs/includes/database.inc on line 235.
# warning: array_keys(): The first argument should be an array in /home/web/html/techs/modules/user/user.module on line 500.
# user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1 query: SELECT p.perm FROM role r INNER JOIN permission p ON p.rid = r.rid WHERE r.rid IN () in /home/web/html/techs/modules/user/user.module on line 500.

The new user account is created properly and subsequent login/logout activity is fine. The warnings only appear at first pubcookie login.

The log entry immediately before the PHP warnings is "Session ID is ..." and immediately after is "User callback received for user N". This suggests that the problem occurs when pubcookie executes

user_external_login_register($pubcookie_user, 'pubcookie');

Similar warnings were a topic of discussion for some Drupal 5 external authentication threads, but I don't know if the issues here are the same.

http://drupal.org/node/109576
http://drupal.org/node/165642